Metal-refractory joint



Sept. 24, 1935. J. E, |ENr'-E| D METAL REFRACTORY JOINT Filed Jun-e 29,1932 INVEN'roR dw. /Us Eos/m l /L /E/VFEL o av v Patented Sept. 24,19.35

Julius Edgar Llllenfeld, Winchester, Mass., as-

signor to Ergon Research Laboratories, Inc., Malden, Mass., acorporation of Delaware Application June 29, 1932, Serial No. 620,051

4 Claims.

The invention relates to ajoint between nonmetallic refractory materialsand certain metals.

While the invention has several objectsfwhich will become apparent inthe following description 5 thereof, it has for its particular objectsthe provision of a mechanically substantial welded joint betweensilicious refractory material and metals having a component suiicientlyelectropositive to react with a silicious component of a refractory, themetal cohering with said refractory by direct molecular contacttherewith; the provision of gas-tight joints of this nature, and moreparticularly the provision of metal to refractory welded joints in whichthe metal has such combined properties of plasticity and expansivitythat during the manufacture and later use of the joint, particularly atelevated temperatures, the stresses induced by reason of the differencebetween the coeilicients of expansion of the metal and the refractory donot fracture the latter nor separate the metal from the refractory; andmore especially the provision of such joints between aluminum and asilicious refractory.

I have found that certain metals having a component suflicientlyelectropositive to react with a silicious component of the refractorymay be welded thereto to accomplish the above objects. Such metals asaluminum and magnesium may, under certain conditions, be caused to thusreact with the refractory forming a silicized transition layer betweenthe metal and the refractory and thus securing molecular contacttherebetween and aording a true welded joint.

Joints of this nature may nd use in many different applications, both asmechanical supports or connections for insulating refractories andjoints that are liquidand/or gas-tight, as for sealing off containers.These welded joints may be utilized, for example, in the suspension ofinsulating bases for high-voltage equipment or terminals for oil-filledtransformers and condenser-s, terminals for pressure-gas-lled tankscontaining transformers, condensers, switches, lightning arresters,etc.; electrodes of electrolytic condensers, resistors, spark plugs,refractory seals and similar devices; also, in connection withhigh-vacuum apparatus, such as Dewar flasks, X-ray tubes and othervacuum discharge devices; mercuryfilled devices operated both in vacuumand/or high-pressure, such as mercuiytoggl? switches, mercuryrectiflers, mercury lamps, etc.

In attaining the above objects, a welded joint is secured as, forexampleV between aluminum and porcelain, in the manner hereinafter morefully set forth and in which' the aluminum, or magnesium, is of suchplasticity and expansivity that it will stand up under the heating andsubsequent cooling of the welding operation without destroying therefractory material or the joint.

It is to be noted that genuinely sealed joints 5 between siliciousinsulators and metals having different coeflicients of expansion haveheretofore been founded upon an entirely different physical basis thanthat herein disclosed. Thus, it has been the practice to join the molteninsulator 10 to the solid metal, whereas in accordance with the presentinvention, the metal is applied in molten condition to a siliciousrefractory. Moreover, the difference in expansion was compenv sated forin the seals of the prior art by utilizing 15 very thin metal, the sealbeing mostly between a metal wall of greatly reduced thicknessand thesilicious insulator whereby the difference of expansion between metaland insulator was accommodated by the inherent elasticity of the 20metal itself.

For this reason, these seals were mechanically vulnerable, due to theextreme thinness' of the metal at the sealingl portion.

In contradistinction to the prior art and in car- 25 i rying out thepresent invention, a welded joint between the metal in a moltencondition and a silicious refractory is provided, the expansiondifferences being accommodated by the inherent plasticity of the metal,rather than by shaping the metal so as to rely upon its elasticity, andysuch that the plastic metal will conform to the stresses induced byreason of the difference between the coefficients of expansion of themetal and the refractory; and thus, by virtue of so conforming, willprevent fracture of the refractory and/or prevent separation of saidrefractory from the metal in securing a molecular contact therebetween.For this reason, a substantial mass of metal at the weld may be obtainedand a rugged joint is secured and may be of such a nature, furthermore,as to be maintained at elevated temperatures.

A further novel characteristic of the joint resides in the fact that thetemperature of the l refractory during the welding action is such as toexceed the melting temperature of the metal to be Welded thereto by anamount suilicientto attain the reaction between the' metal and therefractory, resulting in the formation of the aforesaid transitionlayer. It is to be noted that without such a reaction, a sweated jointrather than a weld would result, which sweated joint could. not have therequired qualities of mechanical strength and/or tightness,A especiallynot at an elevated temperature. g

This application is a continuation in part of my copending applicationsSerial No. 486,101, filed October 3, 1930, and Serial No. 515,885, filedFebruary 14, 1931.

In the accompanying drawing, which illustrates, by way of example,specific embodiments of the novel joint,

Fig. 1 is a front elevation and part vertical section of the riser foran electrode as utilized, for example, in electrolytic condensers.

Fig. 2 is a vertical section of a spark plug embodying the novel joint.

Fig. 3 is a vertical section through the upper` portion of ahigh-pressure gas condenser in which the novel joint is utilized.

Fig. 4 is a vertical section illustrating the application of the noveljoint to a highly evacuated container such as a Dewar fik.

In the provision of these joints between a silicious refractory, such asporcelain, and a metal, such as aluminum, having a componentsufiiciently electropositive to react with a silicious component of therefractory in the manner hereinafter set forth to produce a weld, it isto be noted that by the term "weld or "welded as applied to the jointherein described and referred to in the claims, I wish to be understoodas vhaving reference to the direct consolidation of the two solidbodies-metal and refractory-to the extent of molecular cohesion byfusion at their junction.

Furthermore, as aluminum of different grades gof purity is suitable foreffecting the novel joint,

the characteristics of the Joint being determined to a large degree bythe particular grade of aluminum utilized, I desire, further, to definethe word "aluminum as herein used to include not only substantially purealuminum but also various suitable alloys of aluminum with other metals.

Por example, an alloy of aluminum with 1.25% of manganese; an alloy ofaluminum with 1.25% of manganese and 1% of magnesium; an alloy ofaluminum with 8% of copper, 12V-2% of si1icon and 1.15% of magnesium; analloy of aluminum with 5% silicon; an alloy of aluminum with 5% silicon,1.2% copper, and .5% of magnesium; jan alloy of aluminum with 7% siliconand 0.3% magnesium; an alloy of aluminum with 0.8% of nickel, 0.4% ofiron, and 0.1% of titanium, has been ,found to an'ord satisfactory weldsunder certain conditions. l Also, the term pure aluminum" as utilizedherein is to be understood as referring to aluminum containing 99% orbetter of aluminum and such as is normally produced in the well-knownreduction methods for obtaining aluminum from ;-its ores, while the termhigh purity" aluminum ia intended to refer to the preferred form of purealuminum and containing approximately 99.6% or more of aluminum.

In connection with the degree of purity of the :pure aluminum, it is tobe noted that the amount of the impurities ordinarily present in thealuminum has a deleterious effect on the favorable combination ofplasticity and expansivity and that the higher the degree of purity ofthe aluminum, the greater its plasticity characteristic.

Certain alloys of aluminum compounded so as to make them undesirable forthe use in the novel,v weldin! process do not possess the high degree ofplasticity required for effecting, for ex- .,ample. a Joint which willbe gas-tight on repeated heating and cooling, yet are of such a natureas to afford a suitable joint where these rigid requirements are not metwith. By this I do not wish to necessarily imply that the weld per se isnot perfect and a molecular cohesion is not attained, but rather thatthere may be isolated areas in which no such contact exists and thattherefore these portions might leak.

Particularly in the case of pure aluminum and certain aluminum alloyssuch as aluminum with 1.25% of manganese, and aluminum with 1.25% ofmanganese and 1% of magnesium, is it possible to effect a. joint that isgas-tight and/or one which will not fail under repeated heating andcooling. Where a joint of the very best characteristics is desired,however, high purity aluminum has been found to be the metal best suitedfor this purpose, this being particularly true where the refractory is amaterial such as fused quartz, which is extremely brittle.

The particular grade of aluminum required in connection with theproduction of a joint be tween the same and the selected refractory andwhether the desired characteristic is that of perfect gas tightness, mayreadily be determined. e. g., by welding a threaded aluminum fitting toa tube of the refractory closed on one end, and by connecting saidfitting to a gas pressure tank of, say, Z50-1b. pressure or to a vacuumsystem, and by observing the presence or absence of aleak first at roomtemperature, and secondly at a more elevated temperature which may insome Acases be 80 C., and in other cases run up as high as 300 C. oreven higher.

In carrying out the method for providing the welded joint between asilicious refractory and a metal, an intermediate transition layer ofthe silicized metal is formed which provides molecular contact betweenthe said metal and the said refractory, the reaction between the metaland the refractory being direct. This is best eected by heating therefractory at the area to be welded to a temperature greatly exceedingthe melting temperature of the metal, as to a yellow heat andapproximating 1100* C., which temperature willginsure the aforesaidreaction desired.

The aluminum is also heated and then placed in contact with therefractory whereby the temperature of the aluminum is elevated, eitherby further external heating or from the accumulated heat from therefractory, to an intense degree such as to cause the aluminum to iiowand react with the silicious component of the refractory.

In eii'ecting the weld, it is desirable to coat the aluminum prior toits contact with the heated refractory with a substance which will notdissolve the oxide skin upon the aluminum to a detrimental degree andwhich has a tendency rather to protect the aluminum from oxiizing toodeeply, and to provide an envelope for supporting the metal in a moltenstate even if heated considerably above its melting point.

This envelope should be of a flexible character and I have found that alayer of borax is particularly suitable for this purpose, being whenmolten viscous enough to adhere to the aluminum and at the same timesufficiently liquid to allow the molten aluminum to adjust itself to thecontour of the refractory.

Furthermore, the borax probably facilitates the reaction between thealuminum and the refrac-A tory, as it will run in its molten conditionthe freest at the tip where the aluminum is the thinon the metal andthus causing the latter to flow irregularly in all directions in theabsence of any envelope to restrain it. Such action would be entirelyunsuitable in the present instance.

In contradistinction to the usual method of effecting a joint between ametal and a refractory, I cuse the metal to melt while the refractoryretains its solid phase, and moreover, is

heated to a temperature far above the melting point of the metal whichis to be welded thereto, the particular temperature required being thatnecessary to attain the reaction between the electropositive componentvof the metal and the silicious component of the refractory. Furthermore,the enveloping agent utilized is of such a nature as to melt at thewelding temperature but vnevertheless to adhere to the refractory in amolten condition and to restrain the metal from undue dispersionthereover.

The aforesaid method of welding is applicable to the production of agreat variety of articles and yapparatus utilizing non-metallicrefractory material, having also electrical insulating properties, andmore especially amaterial of this nature having a siliclous component.For example, such refractories as porcelain (Si1limanite) quartz, glassof the borosilicate type, and other silicates have been foundsatisfactory for effecting therewith a welded joint.

The refractory is preferably utilized in cylindricalY form as bushings,tubes, rods, etc.: and the area to be welded is preferably, though notnecessarily, first glazed as by a fluoride or borax glazing.

- As a specifc'example of the application of a welded joint of theaforesaid type an electrode, such as may be utilized for electrolyticcondensers, is shown in Fig. 1. In this embodiment, I0 and I0' designaterespectively the top and bottom aluminum rods or risers of the electrode(not shown) .secured thereto. These risers are secured to or 'areintegral with vend heads, the upper of which is provided with an annularrecess II and projecting axial stem I2, while the lower is provided withthe socket I3.

A conductor I4 for external connection is suit-` rounding wall portionsIl and I3 respectively. t.

The respective refractory members to this end have a snug fit in thecorresponding recess or outer wall thereof which has, previous to theheating operation, applied thereto over the outer surface a coating ofthe ,enveloping agent such as borax.

A welded joint is thereby attained upon heating of the refractory andmetal, as hereinbefore set forth, along the edge of the wall portions I1and I8 to provide convenient external connections to the electrode andamounting of the same.

In Fig. 2 a further embodiment of the invention is disclosed and moreparticularly in connection with the adaptation of the weld to a sparkplug.

Referring to said figure, the axial tubing 20 is 10 of insulatingmaterial such as porcelain .or Sillimanite" and through the same extendsthe conductor or electrode element 2 I which is welded at the one end tothe inside of a cap member or terminal 22. The latter seats over thetube and 15 is shown'as welded along its edge 23 thereto. Furthermore, aweld is effected between the said tube 20 and the aluminum housing 24 ofthe plug through its sleeve 25. The latter may be constituted of themore plastic-type of aluminum 20 andwelded to the portion 24 of theharder type.

Another practical embodiment of the invention is illustrated in Fig. 3in which 30 designates a suitable container adapted to withstand highpressures and, in the present instance, housing 25 the electrodes 3I and3|', of an electrical condenser in which the dielectric between saidelectrodes is constituted by a gas such as nitrogen.. hydrogen, carbondioxide, air, etc., and under extremely high pressure. This necessitatesa se- 30 cure external connection to the electrode or electrodes inorder to avoid wastage or loss of the gas which is to be confinedpennanently'therein. Similar difficulties exist in connection with theoperation of high-voltage transformers with 35 sealed-in fluid,especially such as have a highpressure gas enclosed above the level ofthe fluid; in the operation of electric refrigerators wherein themechanism is hermetically sealed within a gaseous medium under pressure,etc.; as Well as 40 in the case of vacuum-sealed apparatus.

The electrode 3| of the gas condenser is shown connected with a riserextension member 32 which is designed to pass through the top 30' of thecontainer and in such a manner as to be elec- 4:5' trically insulatedtherefrom and sealed against loss of the high-pressure fluid retained bythe container. To this end, a tubular insulator and refractory'member 33is designed to surround a portion of the said riser, more especially thepart 50 ber but is preferably welded to a container of aluminum, asshown, to secure a sealing or gastight fit thereto. This bushing iscounterbored or recessed at its outer end to provide the seat 36 and'asleeve'31 of relatively thin metal. The bottom of the tubular insulatormember 33. moreover, is designed to rest on the seat 38, and. the sleeve31 to fbe welded to the lower end of the said insulator member.

To strengthemlthe mechanical bond between the bushing and insulatormember, more especially with reference to axially directed stresses, itis preferred to provide the lower end of the latter with a peripheralgroove 38 which will be ,substantially filled during the weldingoperation.

cupped for this purpose to afford the overhanging sleeve portion 43embracing said insulator member, and a peripheral groove 44 is providedin the latter to better secure the, cap thereon when welded thereto. Cap40. furthermore, is provided with an inwardly directed threaded boss 4I,which is coaxial with the insulator member and is designed to receivethe outer end of the extension or riser 32 of the electrode, andsuitable electrical connection may then be made to the terminal cap, asat the threaded outer portion 46 thereof.

As an embodiment of a vacuum-sealed apparatus, a Dewar flask orso-called vacuum bottle is illustrated in Fig. 4. In this embodiment thecontainer 50 is of aluminum, and the neck of the same is sealed as at 5Ito a refractory or porcelain mouth element 52 and into which is designedto fit the stopper or cork 53. The enclosing shell 54 for the vacuumchamber, formed between said shell and the container 50, is made also ofaluminum and of two parts in order to admit of the insertion of thecontainer, and at its upper end 1t is welded to the neck member or mouthelement 52 at an area displaced from the portion at which the container50 is welded. The shell 54 may then be closed at the bottom, or in anyconvenient manner, as by welding thereto the cast or forged base 55 ofaluminum. A cap 56 of metal (aluminum) fits over the other end of theflask and is designed to have, for example, a bayonet nt therewith.

I claim:

l. The herein described welded unit comprising a plurality of bodies,one a silicious refractory, the other of a metal of the group comprisingaluminum and magnesium, each body of pre- 4formed individual shape, andan intermediate transitionbond of silicized metal providing molecularcontact between a mass of the said metal small as compared to the totalmass of the metal body and the said refractory.

2. The described welded unit comprising a plurality of bodies, one asilicious refractory, the other of a metal of the group comprisingaluminum and magnesium and of sufficient plasticity to compensate forthe difference between its thermic expansivity and that of therefractory, each body of preformed individual shape, said bodies beingunited molecularly at adjacent surfaces through an intermediatetransition bond of silicized metal providing molecular Contact be tweena mass of the said metal small as compared to the total mass of themetal body.

3. 'Ihe described welded unit comprising a plurality of bodies, one asilicious refractory, the other of a metal of the group comprisingaluminum and magnesium, each body of preformed individual shape, saidbodies being united molecularly at adjacent surfaces through anintermediate transition bond of silicized metal providing molecularcontact between a mass of the said metal small as compared to the totalmass of the metal body and the contact remaining permanent and gas-tightunder repeated heating and cooling.

4. The described welded unit comprising a plurality of bodies, one ofquartz and the other of aluminum, each body of preformedindividualshape, said bodies being united molecularly at adjacent surfaces throughan intermediate transition bond of silicized metal providing molecularcontact between a mass of the said metal small as compared to the totalmass of the metal body.

JULIUS EDGAR LILIENFELD.

